MXPA97001307A - Compositions of latex, double cur - Google Patents

Abstract

Radiation curable latex compositions having a secondary curing mechanism are disclosed. In these compositions, a dispersion made from water, anionically stabilized, of one or more radiation curable resins is combined with a low molecular weight compound having at least two functional reactive groups, wherein one of the functional reactive groups comprises one epoxy and the other functional reactive group comprises both an epoxy and a functionality capable of self-condensing after the formation of the film. Also disclosed is a method for providing a substrate with an interlaced protective coating, wherein a coating of the composition of the present invention is applied to the substrate, the coated substrate is exposed to actinic radiation to effect curing and then the unexposed parts or over exposed coated substrate are cured at room temperature or may

Description

COMPOSITIONS OF LATEX, DOUBLE CURED BACKGROUND OF THE INVENTION The present invention relates generally to latex compositions that are cured by exposure to actinic radiation. Said latex compositions are especially useful in applications for wood or coatings of wood products, as binders for inks and varnishes on forms, and adhesives. The present invention relates particularly to said radiation curable compositions having a secondary curing mechanism, which does not depend on radiation exposure. The primary advantages of the radiation curable compositions are: curing speed; stability and procedural control that is given to the user, especially in high-speed automated procedures. However, these advantages are ineffective due to some significant disadvantages, the most notable being the inability of ultraviolet (UV) radiation to penetrate through the composition itself and the inability to heal in unexposed or "shadowy" regions. In any circumstance, the end result is a coating that has not been cured or over-cured.

Others have attempted to overcome these disadvantages by providing secondary curing mechanisms, which do not depend on exposure to actinic radiation. Sayings products are commonly referred to as "double curing" products. Examples of such secondary mechanisms include: heat curing, using thermal initiators such as peroxides, azo compounds and disulfides; anaerobic curing, where radical initiators (such as peroxides) initiate slow polymerization reactions in air exclusion; Aerobic curing, using metal dryers to initiate oxidative curing; and cured by moisture, using isocyanates or oxazolidines, which react with the humidity of the environment to effect curing. These secondary curing mechanisms were analyzed by John G. Woods in Chapter 9 ("Radiation Curable Adhesives") of Radiation Curing: Science and Technology (Plenum Press: New York, 1992, p . 333-398. The reactions of the epoxy groups with various non-epoxy functional groups, including carboxylic acids, have been used to add the unsaturation pending to the polymer chains, to cure them with actinic radiation; however, in such cases, high manufacturing temperatures usually accelerate the epoxy reaction rate. The epoxy acid reaction is very slow at ambient temperatures and, consequently, is not considered suitable for use as a secondary curing mechanism for many radiation curable adhesives and coatings, since the heat sensitivity of the substrates employed prevents that are cured at high temperatures. See, for example: Ullmann's Encyclopedia of Industrial Chemistry, (Ullman's Encyclopedia of Industrial Chemistry) Ed. 5, vol. A9, p. 556; also see the data in the G. Walz paper, in Proceedings of the International Conference on Organic Coatings Science and Technology (Eleventh International Conference on the Science and Technology of Organic Coatings) (8-12 July 1985), Athens, Greece; p. 429ff.

DECLARATION OF THE INVENTION One aspect of the present invention is directed to radiation curable latex compositions having a secondary curing mechanism, comprising: a dispersion made of water, anionically stabilized, of one or more radiation curable resins; and a low molecular weight compound having at least two functional reactive groups, wherein one reactive functional group comprises an epoxy and the other functional reactive group comprises both an epoxy and a functionality capable of self-condensing after the formation of the film. Another aspect of the present invention is directed to a method that provides a secondary curing mechanism for a radiation curable latex composition, comprising the addition of a low molecular weight compound having at least two functional reactive groups, wherein a functional reactive group comprises an expoxy and the other group Functional reagent comprises both an epoxy and a functionality able to self-condense after the formation of the film. A third aspect of the present invention includes a method that provides a substrate with a protective interlacing coating, comprising the following steps: applying a coating of the composition of the present invention to the substrate; exposing the coated substrate to actinic radiation to effect curing and allowing the unexposed or exposed parts of the coated substrate to cure at room temperature or higher.

DETAILED DESCRIPTION OF THE INVENTION As used in the specification, the following terms have the following definitions, unless the context clearly indicates otherwise. "Latex" or "latex composition" refers to a dispersion of a water insoluble polymer that can be prepared by conventional polymerization techniques such as, for example, emulsion polymerization; on the other hand, "resin" refers to the polymer in the latex. "Interlacing" or "entanglement" refers to the formation of new chemical bonds between the existing polymer chains, and "curing" refers to the entanglement of the polymers after application to the substrate. "Stable to storage" refers to the ability of a composition or formulation of latex to maintain its physical state and application characteristics, and provide films with reproducible properties, during periods of prolonged storage in a container, before application to the substrate. "Life in the container" or "shelf life" refers to the period of time in which a composition is stable to storage. "Two-pack" or "two-pack" refers to the coating compositions (or systems) with a relatively short life in the container. In general, components of two-component systems are stored separately, then mixed together shortly before use. On the other hand, "of a package" or "of a component" refers to coating compositions with a long shelf life, so that the components can be stored together in a container. The specified indices should be understood as inclusive unless they are uniquely identified otherwise. In the present invention, the resins include, but are not limited to: addition polymers of at least one ethylenically unsaturated monomer; condensation polymers made by the reaction of one or more diisocyanates or polyisocyanates with one or more compounds containing groups with active hydrogens; and polyester resins made by the reaction of one or more alcohols, especially diols or polyols, with polyhydric acids or polybasic acid anhydrides. Said addition polymers include, for examples are those prepared from acrylic ester monomers including methyl acrylate, ethyl acrylate, butyl acrylate, 2-ethylhexyl acrylate, methyl methacrylate, butyl methacrylate; styrene or substituted styrenes; butadiene; vinyl acetate and other vinyl esters; vinyl monomers such as chloride, vinylidene chloride, pyrrolidone N-vinyl; and acrylonitrile or methacrylonitrile. Condensation polymers include, for example, polyurethanes and polyureas such as those made by the reaction of one or more diisocyanates or polyisocyanates with one or more compounds containing groups with active hydrogens such as, for example, polyester, polycarbonate or polyether di or polyols, monomeric alcohols, diols or polyols, primary or secondary amines or hydrazine compounds, mercaptans or compounds containing enol hydrogens such as acetoacetate groups; Likewise included are polyester resins made by the reaction of one or more alcohols, especially diols or polyols, with polyhydric acids or anhydrides of polybasic acids, such as, for example, reaction products of ethylene glycol, propylene glycol, isomeric butanediols or hexanediols, glycerol, neopentyl glycol, allyl alcohol, trimethylolpropane, diethylene glycol, triethylene glycol, propylene glycol or polyether oligomers made by the condensation of one or more of these alcohols, with acids or acid anhydrides such as adipic acid, maleic acid, maleic anhydride, phthalic acid, phthalic anhydride, tetrahydrophthalic acid, tetrahydrophthalic anhydride, trimellitic anhydride, acrylic acid, methacrylic acid, fumaric acid, itaconic acid or natural oil fatty acids such as flaxseed oil fatty acids, oil fatty acids high, fatty acids of soybean oil or abietic acid. Polyester resins or their precursors can also be made using transesterification reactions using methods well known in the art for the reproduction of alkyd polyesters. The dispersions of these resins can take the form of single or multiple stage particles. The multistage particles will comprise at least two mutually incompatible copolymers having any number of morphological configurations, for example: core / shell; core / shell particles with cover stages that incompletely encapsulate the core; core / shell particles with a multiplicity of nuclei that interpenetrate the network of the particles; and the like, wherein most of the surface area of the particles will be occupied by at least one outer stage and the interior of the particle will be occupied by at least one interior stage. For the addition polymers included in the present invention, anionic stabilization can be conferred through the co-polymerisation of low levels of ethylenically unsaturated acid monomers (eg, from 0.1 to 7% by weight). weight, based on the weight of the addition polymer). Examples of ethylenically unsaturated acid monomers useful in the present invention include, but are not limited to: acrylic acid, methacrylic acid, crotonic acid, itaconic acid, fumaric acid, maleic acid, monomethyl itaconate, monomethyl fumarate, maleic anhydride, acid 2-acrylamide-2-methyl-l-propanesulfonic acid, sodium vinyl sulfonate and phosphoethyl methacrylate. For the polyurethane condensation polymers included in the present invention, anionic stabilization can be conferred through the copolymerization of acid-containing compounds in the polymer backbone, such as, for example, from 0.1 to 15% by weight, based on the weight of the polyurethane polymer, dimethylolpropionic acid or its sulphonic acid analog. For the polyester condensation polymers included in the present invention, the anionic stabilization can be conferred through the use of a molar excess of functional acid groups during the polymerization of the resin, so that the resin has an acid equivalent weight between about 600 and 20,000 (for resins reducible in water, preferably between approximately 900 and 1400). The polymers are curable by radiation through the incorporation of ethylenically unsaturated groups, which can either be incorporated directly into the polymer backbone during their manufacture or be added to the polymer skeleton to some subsequent point. Examples of stabilized anionic-stabilized radiation curable polymers useful in the present invention include, but are not limited to, those disclosed and described in: US Patent No. 4,287,039 (Buethe et al.), DE4,011,353 and DE4,011,349 (Kressdorf et al.), DE4,031,732 and DE 4,203.54β (Beck et al.), EP399,160 (Flakus), EP 392,352 (Haberle et al.), EP 518,020 (Flakus), US 5,306,744 (Wolfersberger et al.), US 4,730,021 (Zom et al.), US 4,107,013 (McGinniss et al.), US 5,371,148 (Taylor et al.), WO 95/00560 (Johnson et al.) And EP 442,653 (Pears et al.). to the.). The contents of these patents and patent applications are incorporated herein by reference. Depending on the particular use, the resins useful in the present invention will usually be replaced by aqueous dispersions at solid levels between about 20% by weight and 70% by weight, or in reducible form in water (with or without a cosolvent) at levels solids between about 50% by weight and 100% by weight. The level of solids preferred for the application of coatings depends on the requirements of the particular application. For those applications where a low solids coating is preferred, it is preferred to use formulations between 5% by weight and 60% by weight polymer solids, more preferably between about 20% by weight and 50% by weight. High solids coatings are preferably formulated at levels solids in excess of 60%, more preferably between 80 and 100% by weight. The low molecular weight epoxy-containing compounds of the present invention contain: at least two epoxy functional groups (eg, groups containing an oxirane ring); or at least one epoxy group and at least one other functional group capable of carrying out the condensation reaction with itself or with some reactive functionality in the backbone of the resin. The molecular weight of said compounds is preferably less than 1000, more preferably at an index of 100 to 500. Preferred epoxy-containing compounds include, but are not limited to: aliphatic or cycloaliphatic di- and tri-epoxies, such as carboxylate 3, 4-epoxycyclohexylmethyl-3, 4-epoxycyclohexane or bis- (3, -epoxycyclohexyl) adipate; and epoxysilanes such as 3-glycidoxypropyltrimethoxysilane or other glycidoxyalkyl trialkoxysilanes. The epoxy compounds are added to the resin using methods known to those skilled in the art. For compositions of a package, the simplest method is to slowly add an appropriate amount of the epoxy compound to the appropriate amount of the resin under conditions of good distribution mixing, then continue to stir for a period of typically 10 minutes at three hours. For two-pack compositions, the epoxy compound can be added by the end user, under conditions of good mixing of distribution, to a previously formulated paint, varnish or coating. In such cases, it may be preferable to allow the resin mixture to equilibrate with epoxy for several hours or overnight, before application to the substrate. The container life obtained with the compositions of the present invention may be several weeks. Compositions of two packages can also be mixed using equipment for application of plural components, in in-line mixers and so on using mixing and application methods which are well known in the art. Typical levels of use for the epoxy compounds of the present invention are between 0.2 to 1.5 epoxy equivalents per equivalent of resin acid, depending on the epoxy and the particular use of the resulting latex. The equivalent weights of the resin acid can be determined by means of a direct titration method, such as that described in ASTM D4370-84 or, alternatively, acid numbers supplied by manufacturers can also be used. On a weight basis, the levels of the epoxy compound can be about 0.5 and 10% by weight, based on the total weight of the polymer. Surfactants are commonly used in emulsion or dispersion polymerization to provide stability, as well as to control particle size. Surfactants can also provide dispersibility to the resins reducible in water. Conventional surfactants include anionic or nonionic emulsifiers, or combinations thereof. Typical anionic emulsifiers include, but are not limited to: alkyl ammonium or alkali sulfates, alkyl sulfonates, salts of fatty acids, esters of sulfosuccinic acid salts, alkyl diphenylether disulfonates and salts or free acids of phosphate esters of organic complex. Typical nonionic emulsifiers include, but are not limited to: polyethers, e.g. , condensates of ethylene oxide and propylene oxide, which include ethers and thioethers of polypropylene glycol and straight or branched chain alkyl and alkylaryl polyethylene glycol, phenoxypoly (ethyleneneoxy) alkyl ethanols, having alkyl groups containing about to about 18 carbon atoms and have from about 4 to about 100 ethyleneoxy units, and polyoxy-alkylene hexitrogen derivatives, including sorbitans, sorbides, mannites and mannides. The surfactants can be employed in the compositions of the present invention at levels of 0.1 to 3% by weight or greater, based on the total weight of the final composition. The compositions of the present invention may contain photoinitiators or combinations of photoinitiators and photoactivators, to promote the curing of the coating in those parts of the coating that are exposed to the actinic radiation. Typical levels of use for photoinitiators are from 0.1 to 6% by weight, based on the non-volatile material, preferably approximately 0.5 to 4.0% by weight. Examples of said photoinitiators include benzophenone and substituted benzophenones, benzoin and its derivatives, such as benzoin butyl ether and benzoin ethyl ether, benzyl ketal, such as benzyl dimethyl ketal, acetophenone derivatives such as a, a-diethoxyacetophenone and, a-dimethyl-a-hydroxyacetophenone, benzoates such as methyl benzoate or benzoyl, thioxanthones, Michler's ketone and acylphosphine oxides or bis-acylphosphine oxides. Other optional components of the compositions of the present invention include, but are not limited to: co-solvents and coalescents, pigments, fillers, dispersants, moisture agents, anti-foam agents, UV absorbers, antioxidants, biocides and stabilizers. These optional components (as desired) can be added in any order of addition, which does not cause any incompatibility between the components. Components that do not dissolve in the aqueous carrier (such as pigments and fillers) can be dispersed in the latex or in an aqueous or cosolvent carrier, using a high shear mixer. The pH of the composition can be adjusted by adding acid or base, with stirring. The base examples include, but are not limited to ammonia, diethylamine, triethylamine, dimethylethanolamine, triethanolamine, sodium hydroxide, potassium hydroxide and sodium acetate. Examples of acids include, but are not limited to, acetic acid, formic acid, hydrochloric acid, nitric acid, and toluene sulfonic acid. The formulated coating compositions can be used as top coatings, intermediate coatings or primary coatings, and are useful as: paints, including wood coatings; pigments; varnishes; adhesives; inks, including screen or gravure printing inks and flexographic printing inks; plastics, including plastic sheets and polyvinyl chloride floor; fiber; paper, including overprint varnishes for paper and cardboard; skin; and photoresistors for the concealment of welding in electronic circuits, printing plates and other compounds that use ultraviolet curing. These coatings are particularly useful in wood applications, such as, for example, in cabinets, furniture and floors. The compositions of the present invention can be applied to desired substrates, using conventional application techniques such as conventional or airless spray, roller, brush, curtain, fluid, bubble, disc and deep coating methods. Once applied to the substrate, the compositions are cured by exposure to radiation after most or all of the water has evaporated from the composition. Useful forms of radiation include radiation by ionization, radiation by electron beam and ultraviolet radiation. Sources of ultraviolet radiation include sunlight, mercury vapor lamps, carbon arc lamps, xenon lamps and the like. It is preferable to use mercury vapor lamps.

The following examples are presented to illustrate other various aspects in any respect. In Examples 1 and 2, below, tests for resistance to deterioration and stain resistance were conducted in various latexes, with or without secondary curing mechanisms of the present invention, for comparison purposes. The test methods and formulations for latex control used in these Examples are described as follows. Deterioration Resistance Test - The film is scraped vigorously with the nail for several times, then it is rated according to the mark left on the film. The spots were visually assessed on a scale of 0 to 10, where 10 indicates that no traces remained on the film. Stain Resistance Test - Stain tests were developed in accordance with ASTM D1308-87. The spots were visually assessed after recovery using a scale of 0 to 10, where 0 equals complete destruction of the coating and 10 equals no effect on the test solution.

Latex A is an acrylic latex curable by radiation, formed by the production of a double-stage polymer of the entire composition of 48% by weight of butyl acrylate, 24% by weight of styrene, 25.5% by weight of methacrylic acid and 2.5% allyl methacrylate, the neutralization of 15% of the acid equivalents with ammonium hydroxide, the addition of an amount of glycidyl methacrylate, corresponding to 74 percent in ols of the acid, and the reaction at approximately 80 ° C, until essentially all the glycidyl methacrylate has reacted. The resulting latex had a solids content of 40.2% by weight, an equivalent methacrylate weight of 592, based on the dry polymer (for UV curing), and an acid number of 58, based on the dry polymer. Latex B, for comparison purposes, is a non-radiation curable latex, which is formed with the preparation of a single stage polymer of butyl acrylate and methyl methacrylate, with a glass transition temperature of 55 ° C. The resulting latex had a solids content of 37% by weight, without residual methacrylate functionality and an acid number of 52, based on the dry polymer. It was neutralized with ammonia at a pH of 7.0 and formulated according to the following table.

INGREDIENT Quantity (% by weight) Latex B 202.7 Glycol monobutyl ether 9.75 ethylene Ethylene glycol ethylhexyl 1.50 ethylene isopropanol 11.25 Water 63.1 7% ammonia solution 20.0 Example 1: Latex with Epoxysilane For this example, 3-glycidioxypropyltrimethoxysilane ("GPMS") was added to Latex A at equivalent levels of 25% and 50% (2.3% by weight and 4.5% by weight, respectively, based on weight of Latex A moist). The solids were kept constant at 40% with the addition of water, as was necessary. The epoxysilane was easily stirred, without any apparent shock to the latex. The adduction preparations remained fluid, without mud formation or apparent viscosity, for at least several weeks. When the formulations were 7 days old, they were applied to give an appearance of cherry wood, using a roller (two layers). Latex A alone (without photoinitiator) and Latex B (a thermoplastic formulation not curable by radiation) were also applied as controllers. Then, the films were aged 3 days at 60 ° C to simulate an extended curing at room temperature. Subsequently, the films were tested and gave the following results.

Latex A Latex A + 0 .25eq Latex A + Latex B only GPMS 0.5eq GPMS Spot test of 16 hours Water 9 9 10 10 1% Dreft detergent 5 8 8 7 Vinegar 9 10 10 9 One-hour stain test 50% EtOH 8 9 10 4 3A EtOH 1 7 8 0 7% Ammonia 1 3 4 1 Resistance to Deterioration 6 6 9 4 While Latex A only developed well after the accelerated three-day cure, the rise in epoxysilane was very evident. With the addition of epoxysilane, Latex A films passed to latex B film by a large margin in base strength, alcohol resistance and deterioration resistance.

Example 2: Latex with Diepoxy For this example, an aliphatic diepoxy (3,4-epoxycyclohexylmethyl-3, 4-) was stirred in Latex A. cyclohexylcarboxylate). The formulations were prepared at 50% and 100% equivalents (2.7% by weight and 5.3% by weight, respectively, based on the weight of the wet Latex A). The solids were kept constant at 40% with the addition of water, as was necessary. The epoxysilane was easily stirred, without any apparent shock to the latex. The adduction preparations remained fluid, without mud formation or apparent viscosity, for at least several weeks. When the formulations were 24 hours old, they were applied to give an appearance of cherry wood, using a roller (two layers). The same controllers of Example 1 were used for this Example. The films were aged 3 days at 60 ° C to simulate an extended curing at room temperature. Next, the films were tested and gave the following results.

As in Example 1, Latex A only developed well; however, the addition of diepoxy considerably increased its development to very surprising levels in comparison to those achieved with Latex B film.

Claims (10)

1. CLAIMS 1. A radiation curable latex composition having a secondary curing mechanism, comprising: a dispersion made of water, anionically stabilized, from one or more radiation curable resins; and a low molecular weight compound having at least two functional reactive groups, wherein one functional reactive group comprises an epoxy and the other functional reactive group comprises both an epoxy and a functionality capable of self-condensing after the formation of the film.
2. 2. The latex composition according to claim 1, wherein the low molecular weight compound having at least two functional reactive groups is selected from the group consisting of: aliphatic or cycloaliphatic di- and tri-epoxies, and epoxysilanes.
3. 3. The latex composition according to claim 2, wherein the low molecular weight compound having at least two functional reactive groups is selected from the group consisting of: 3,4-epoxycyclohexylmethyl-3-epoxycyclohexane carboxylate, bis - (3, 4-epoxycyclohexyl) adipate, 3-glycidoxypropyltrimethoxysilane and other glycidoxyalkyl trialkoxysilanes.
4. 4. The latex composition according to claim 1, wherein the molecular weight of the low molecular weight compound is 1000.
5. 5. The latex composition according to claim 4, wherein the molecular weight of the low molecular weight compound is from 100 to 500. The latex composition according to claim 1, wherein the composition has a container life of at least two weeks. A method that provides a secondary mechanism for curing a radiation curable latex composition, comprising the addition of a low molecular weight compound having at least two functional reactive groups, wherein a functional reactive group comprises an epoxy and the other functional reactive group comprises both an epoxy and a functionality capable of self-condensing after the formation of the film. The method according to claim 7, wherein the low molecular weight compound having at least two functional reactive groups is selected from the group consisting of: aliphatic or cycloaliphatic di- and tri-epoxies, and epoxysilanes. 9. The method according to claim 8, wherein the low molecular weight compound having at least two functional reactive groups is selected from the group it consists of 3,4-epoxycyclohexylmethyl-3,4-epoxycyclohexane carboxylate, bis- (3, 4-epoxycyclohexyl) adipate, 3-glycidoxypropyltrimethoxysilane and other glycoxyalkyl trialkoxysilanes. 10. A method for providing a substrate with an interlaced, protective coating, comprising the following steps: applying a coating of the composition of claim 1 to the substrate; exposing the coated substrate to actinic radiation to effect curing; and allowing the unexposed or over exposed parts of the coated substrate to cure at room temperature or higher.